Reuse pattern network scheduling using interference levels

ABSTRACT

Interference levels occurring at one or more stations are mapped, and a reuse pattern is generated, based on the mapped interference levels, including one or more reuse sets of stations capable of sharing a transmission resource. The stations within each reuse set are listed in increasing order based on their respective interference levels, and an additional station is added to a reuse set, as long as the cumulative interference level within the reuse set is below a threshold interference level and the additional station is not already listed in another reuse set. A network schedule is updated based on the reuse pattern to increase bandwidth efficiency in the network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/777,385, filedJul. 13, 2007, which is incorporated herein by reference in itsentirety. Moreover, this application is based on, and claims the benefitof, U.S. Provisional Application titled “REUSE PATTERN NETWORKSCHEDULING ALGORITHM FOR OFDMA NETWORKS USING RELAY STATIONS”, U.S. Ser.No. 60/864,498, filed Nov. 6, 2006, inventors Chenxi Zhu, Dorin Viorel,Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, Attorney Docket No.1974.1009P, and which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION Description of the Related Art

Wireless communication networks have become increasingly popular andgenerally include a base station that provides service to a cell arealocated around the base station. Subscriber stations, including mobilestations (such as cell phones, etc.), are able to communicate with thebase station when they are within the service area (such as the cellarea) of the base station.

Interference among stations in the same or different cells of thenetwork can cause significant problems. The use of relay stations in thenetwork can complicate interference problems.

SUMMARY OF THE INVENTION

Various embodiments of the present invention provide a method andapparatus which (a) maps interference levels occurring at one or morestations in a wireless network; and (b) generates a reuse set, based onthe mapping, of stations, included in said one or more stations, capableof sharing a transmission resource.

Various embodiments of the present invention provide a method andapparatus which (a) maps interference levels occurring in one or morestations in an Institute of Electrical and Electronics Engineers (IEEE)802.16 system, each station of said one or more stations being a basestation or a relay station; and (b) generates a reuse pattern, based onthe mapping, including one or more reuse sets of stations, included insaid one or more stations, capable of sharing a transmission resource.

The above embodiments of the present invention are simply examples, andall embodiments of the present invention are not limited to theseexamples or to including all the features described in the Summary ofthe Invention section of this application.

Additional features of the invention will be set forth in part in thedescription which follows, and, in part, will be obvious from thedescription, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an example of a wireless network topologyinvolving a base station, a network management entity (such as a basestation controller) and three relay stations operating in an OFDMAnetwork under the IEEE 802.16j standard.

FIG. 2 is a flowchart illustrating the method of mapping interferencelevels occurring at one or more stations in a wireless network andgenerating a reuse set, according to embodiments of the presentinvention.

FIG. 3 is a flowchart illustrating the method of generating a reuse set,according to embodiments of the present invention.

FIG. 4 is a flowchart illustrating the method of generating one or aplurality of reuse sets and a reuse pattern used to update a networkschedule, according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tolike elements throughout.

In wireless communication networks, due to such effects as shadowingarising from blockage by buildings and other obstructions betweentransmission/reception antennas, there exist dead zones in whichcommunication with the base station is not possible, despite beingwithin the service area. To combat this problem, in a wireless network,such as for example, an Orthogonal Frequency Division Multiple Access(OFDMA) network, relay stations can be employed for providing enhancedtransmission capabilities by acting as intermediaries between mobilestations operating in the network and the base station. In this manner,a mobile station that is incapable of connecting directly to a basestation within its cell service area may still connect indirectly to thebase station by first communicating with a relay station that does havea direct link, or possibly an indirect link through additional relaystations, to the base station.

A problem arises, however, in that greater levels of interference areproduced in the network with the addition of base and relay stations.Spatial reuse of the spectrum in the network is required to increase thespectrum efficiency and total capacity of the network, subject to therequirement the interference caused by concurrent transmissions needs tobe carefully managed. Since the increased intranet interference degradesthe carrier to interference-plus-noise ration (CINR) for the impactedlinks, properly scheduling the concurrent transmissions to mitigate theinterference levels impacts directly the quality of service (QoS) onthese links.

Therefore, a network entity schedule algorithm can be defined thatreduces the intranet interference between different stations (eitherbase stations or relay stations) operating within the wireless network(e.g., an OFDMA network) while at the same time maximizes the spatialreuse of the radio resource, thereby optimizing CINR degradation andthus allowing higher coding rates to be used on the impacted links.

FIG. 1 is an illustrative example of a wireless network topologyinvolving a base station and three relay stations operating in an OFDMAnetwork. The network cell includes a base station (BS) 10, a first relaystation (RS1) 20, a second relay station (RS2) 21, a third relay station(RS3) 22 and a network management entity 30. This example topology isintended to show a single possibility of a network cell, and embodimentsof the present invention are not limited to any particular topology. Forexample, embodiments of the present invention are not limited to anetwork with the specific number of base and/or relay stations in thespecific configuration shown in FIG. 1.

In the specific example in FIG. 1, RS1 20 can communicate directly withBS 10 via the transmission link between BS 10 and RS1 20, or indirectlyvia the transmission link from BS 10 to RS2 21 and then through thetransmission link from RS2 21 to RS1 20.

Various embodiments of the present invention assume a fixed reusepattern. That is, the base stations and relay stations are assumed to bein fixed positions and each transmitter (either a base station or arelay station) transmits with a fixed power assigned by networkmanagement entity 30. However, the present invention is not limited to afixed reuse pattern.

As the algorithms described herein are computationally demanding,various embodiments of the present invention are intended for use innetworks where, for example, each base station and relay stationgenerates its own transmission schedule. However, the present inventionis not limited to each base and relay station generating its owntransmission schedule.

FIG. 2 is a flowchart illustrating a method of mapping interferencelevels occurring at one or more stations in a wireless network andgenerating a reuse set, according to embodiments of the presentinvention. Referring now to FIG. 2, at operation 110, interferencelevels occurring at one or more stations in a wireless network aremapped.

For example, network management entity 30 (see FIG. 1) produces a mappedinterference matrix based, for example, on noise plus interferencemeasurements performed by different stations (e.g., base station 10)positioned within a cluster of cells subject to the interferencemapping. That is, the interference matrix includes the noise plusinterference generated by each station upon each other station.

A mapping interference mode is, for example, a maintenance type ofoperation, in which an implementation-specific network interferencemapping pattern is transmitted from a station using, for example, fixedpower. As an example, each relay station within the cluster of cellssubject to the interference mapping transmits within the same uplink(UL) frame, a specific UL interference pattern based, for example, on aspecific UL sounding sequence. Upon receiving the UL interferencepatterns, all stations within the cluster of cells execute, for example,burst noise power measurements on the received UL interference patterns.Of course, the present invention is not limited to any particular ULinterference pattern based on any specific UL sounding sequence, or tostations executing any particular burst noise power measurements.

For example, the burst power measurements executed by the stations areimplementation specific and could include, for example, Received SignalStrength Indication (RSSI) measurements or, for example, Signal toInterference Plus Noise Ration (SINR) measurements. These burst powermeasurements are, for example, proportional with the interference pathbetween stations sending and receiving the UL interference patterns. Ofcourse, the present invention is not limited to any particularmeasurements being included in the executed burst power measurements.

According to various embodiments of the present invention, the networkinterference mapping pattern is scheduled, for example, periodically bynetwork management entity 30. Each base station (e.g. base station BS10) then, for example, averages the burst power measurements from eachstation and transmit the averaged measurements to network managemententity 30 to generate the interference matrix. However, the presentinvention is not limited to periodic scheduling of network interferencemapping, or to any particular types of calculations.

An example interference matrix (INT) shown below maps the noise plusinterference caused by each station upon each other station in thewireless network. As shown in this example, NI_(ij) represents the noise(N) plus interference (I) caused by station “i” upon station “j”. Theeffect is not necessarily symmetrical due to the potential differenttransmission powers of the stations, although it is assumed that eachtransmitter transmits with a fixed power. This example shows a squareY×Y matrix, but the matrix could also be an Y×M matrix.

${INT} = \begin{bmatrix}{NI}_{1,1} & {NI}_{1,2} & {NI}_{1,3} \\{NI}_{2,1} & {NI}_{2,2} & {NI}_{2,3} \\{NI}_{3,1} & {NI}_{3,2} & {NI}_{3,3}\end{bmatrix}$

The above-described mapping the interference levels by estimation of theinterference matrix is described, for example, in U.S. ProvisionalApplication No. 60/864,491, titled “INTERFERENCE MAPPING PROCEDURE FOROFDMA NETWORKS USING RELAY STATIONS”, inventors Chenxi Zhu, DorinViorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, filed Nov. 6,2006, attorney docket number 1974.1007P, and U.S. ProvisionalApplication No. 60/891,096, titled “INTERFERENCE MAPPING PROCEDURE FOROFDMA NETWORKS USING RELAY STATIONS”, inventors Chenxi Zhu, DorinViorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, filed Feb. 22,2007, attorney docket number 1974.1020P, and U.S. utility patentapplication titled “INTERFERENCE MEASURING AND MAPPING METHOD ANDAPPARATUS FOR WIRELESS NETWORKS USING RELAY STATIONS”, U.S. Ser. No.11/777,566, inventors Chenxi Zhu, Dorin Viorel, Jagan Seshadri, JonathanAgre and Wei-Peng Chen, attorney docket number 1974.1020, filed Jul. 13,2007, and which are incorporated herein by reference in their entirety.However, the present invention is not limited to this specific manner ofmapping the interference levels, and other manners of mapping theinterference levels can be implemented. More specifically, the presentinvention is not limited to the mapping the interference levels byestimation of the interference matrix as described above, and in U.S.Provisional Application No. 60/864,491, titled “INTERFERENCE MAPPINGPROCEDURE FOR OFDMA NETWORKS USING RELAY STATIONS”, inventors ChenxiZhu, Dorin Viorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen,filed Nov. 6, 2006, attorney docket number 1974.1007P, and U.S.Provisional Application No. 60/891,096, titled “INTERFERENCE MAPPINGPROCEDURE FOR OFDMA NETWORKS USING RELAY STATIONS”, inventors ChenxiZhu, Dorin Viorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen,filed Feb. 22, 2007, attorney docket number 1974.1020P, and U.S. utilitypatent application titled “INTERFERENCE MEASURING AND MAPPING METHOD ANDAPPARATUS FOR WIRELESS NETWORKS USING RELAY STATIONS”, U.S. Ser. No.11/777,566, inventors Chenxi Zhu, Dorin Viorel, Jagan Seshadri, JonathanAgre and Wei-Peng Chen, attorney docket number 1974.1020, filed Jul. 13,2007. Accordingly, the present invention is not limited to anyparticular manner of mapping interference levels in operation 110.

From operation 110, the process moves to operation 120, where a reuseset of stations capable of sharing a transmission resource is generatedbased on the mapping operation 110. Specific operations of generatingthe reuse set are described in detail with reference to FIG. 3 describedbelow.

FIG. 3 is a flowchart illustrating a method of generating a reuse set,according to an embodiment of the present invention. Referring now toFIG. 3, in operation 210, the one or more stations within the wirelessnetwork are sorted, for example, by network management entity 30 in, forexample, increasing order based on their respective interference levelsmapped by operation 110 (see FIG. 2) described above. The presentinvention is not limited to sorting in an increasing order, and othervariations of a sorting procedure can be implemented. In addition, thesorting is not limited to being performed by network management entity30, and could be performed by other entities in the network.

From operation 210, the process moves to operation 220, where networkmanagement entity 30 determines, for example, the station with thelowest interference level (i.e., the smallest NI_(ij)), based on themapping operation 110, and this station is added to the reuse set. Thepresent invention is not limited to determining the station with thelowest interference level, and other variations can be implemented,based on the sorting procedure implemented in operation 210. Inaddition, the determination is not limited to being performed by networkmanagement entity 30, and could be performed by other entities in thenetwork.

From operation 220, the process moves to operation 230, in which it isdetermined, using the sorting procedure 210, whether the station withthe next lowest interference level is unassigned to a reuse set andwhether the cumulative interference level within the reuse set currentlybeing generated would be below a threshold interference level for allthe stations already in the reuse set and for the station underconsideration for being added to the reuse set if the station with thenext lowest interference level is added to the reuse set currently beinggenerated.

The threshold interference level is a predetermined level set by, forexample, the network management entity 30 (see FIG. 1). The thresholdinterference level is, for example, fixed and is determined, forexample, by simulations based on an effective coding rate calculated byaveraging transmission rates to mobile stations by the base and/or relaystations. The threshold interference level reflects, for example, themaximal total interference that a downlink transmitter (a base stationor a relay station) can tolerate is allowed to cause to other cellssharing the same spectrum. The network management entity 30 is capableof determining, for example, the maximal transmission power used by eachbase and relay station. However, the present invention is not limited tothe predetermined level of the threshold interference level being set bythe network management entity 30 or to being fixed or to beingdetermined based on any particular simulation.

If both of the conditions checked in operation 230 are not met, theprocess moves to operation 250, where it is checked if every station hasbeen either assigned to a reuse set (including previous constructedreuse sets and the current one), or is not eligible to the current reuseset. If both conditions are not met, the process returns to operation230, where the next station in the sorted list of stations, with a nextlowest interference level, is checked to determine whether it is alreadyassigned to a reuse set or the cumulative interference level within thereuse set currently being generated would be below a thresholdinterference level if the current station being checked is added to thereuse set currently being generated.

If both of the conditions checked in operation 230 are satisfied, theprocess moves to operation 260 in which the station being checked is,for example, added to the reuse set currently being generated. Fromoperation 260, the process moves to operation 250, where it isdetermined, for example, whether all stations are assigned to a reuseset.

The process including operations 230, 250 and 260 is reiterated, forexample, until all stations have been either assigned to a reuse set ordetermined not eligible to any reuse sets constructed as determined byoperation 250. When operation 250 determines that, for example, allstations are assigned, the process of constructing a reuse set ends. Theprocess may repeat and generate a reuse set each time, until allstations have been assigned to some reuse set.

The process illustrated in FIG. 3 assures that each generated reuse setincludes as many stations (relay and/or base stations) as possible,while still having a cumulative interference level below the thresholdinterference level. Thus, each generated reuse set includes the maximumnumber of stations while tolerating the cumulative interference whentransmitting with a predetermined effective coding rate and transmissionpower. As a result, each generated reuse set includes one or morestations which are capable of sharing a transmission resource, includinga frequency or a timeslot, or a combination of both.

Of course, the process in FIG. 3 is only one example of a process togenerate a reuse set, and many variations are possible. The presentinvention is not limited to the specific example in FIG. 3. For example,the present invention is not limited to including each of the specificoperations in FIG. 3. Moreover, there are many variations of thespecific operations in FIG. 3 that can be implemented.

FIG. 4 is a flowchart illustrating the method of generating one or aplurality of reuse sets and a reuse pattern used to update a networkschedule, according to an embodiment of the present invention. Referringnow to FIG. 4, operation 310 represents the generation of one or aplurality of reuse sets using the reuse set generation operationdescribed above (see FIG. 3).

From operation 310, the process moves to operation 320, in which, forexample, any empty reuse sets (i.e., reuse sets including no basestations or relay stations) are removed.

From operation 320, the process moves to operation 330, in which, forexample, the remaining reuse sets are grouped to form a reuse pattern,including one or a plurality of reuse sets.

From operation 330, the process moves to operation 340, where, forexample, the network management entity 30 or a base station 10 (seeFIG. 1) generates a network schedule including the radio resources thatbase station and relay stations in each respective reuse set is allowedto use for its downlink access. The bandwidth can be efficientlyallocated using, for example, the reuse pattern by assigning resourcesto individual reuse sets including a maximum number of base stations andrelay stations, while, for example, maintaining a cumulativeinterference level below the predetermined threshold interference level.As an example, each station generates its own transmission scheduleusing the radio resource assigned to it by, for example, networkmanagement entity 30 or a base station 10.

From operation 340, the process moves to operation 350, where networkmanagement entity 30 or the base station 10 waits, for example, for apredetermined period of time before updating the network schedule. Thebase station may update the network interference matrix by having thetransmission stations estimate the interference from other transmissionstations, and collect and update the network load and/or congestioninformation. Because the computations at network management entity 30 orthe base station 10 are intensive, the update may take place, forexample, over tens of frames. For example, the network schedule can beset to update every ten seconds. However, the present invention is notlimited to any particular period of time before updating the networkschedule.

From operation 350, the process moves to operation 360, where thenetwork schedule is updated after a predetermined period of time inorder to assure that the network schedule optimally allocatestransmission resources, based on the reuse pattern.

Of course, the process in FIG. 4 is only one example of a process togenerate one or a plurality of reuse sets and a reuse pattern. Thepresent invention is not limited to the specific example in FIG. 4. Forexample, the present invention is not limited to including each of thespecific operations in FIG. 4. Moreover, there are many variations ofthe specific operations in FIG. 4 that can be implemented.

Various embodiments of the present invention provide a method andapparatus which (a) maps interference levels occurring at one or morestations in a wireless network; and (b) generates a reuse set, based onthe mapping, of stations, included in said one or more stations, capableof sharing a transmission resource. Although not limited to anyparticular type of wireless network, various embodiments of the presentinvention are applicable for use within an IEEE 802.16 system, whereeach of the one or more stations is a base station or a relay station.

Various embodiments of the present invention provide a method andapparatus in which generating a reuse set includes (a) sorting one ormore stations in increasing order based on their respective mappedinterference levels; (b) beginning with a station, among the one or morestations, with the smallest interference level, adding the station tothe reuse set; (c) adding an additional station with a next lowestinterference level to the reuse set, as long as a cumulativeinterference level for every station within the reuse set is below athreshold interference level and the additional station is not alreadyassigned to another reuse set; and (d) repeatedly adding an additionalstation, as described above, until each of the one or more stations isincluded in a reuse set.

Various embodiments of the present invention provide a method andapparatus which (a) generates a reuse pattern comprising one or aplurality of reuse sets; and (b) updates a network schedule, by anetwork management entity, based on the reuse pattern, to increasebandwidth efficiency.

Various embodiments of the present invention provide a system forgenerating a reuse group based on interference levels in an IEEE 802.16network. In various embodiments of the present invention, the system (a)maps interference levels, occurring at one or more stations, each ofsaid one or more stations being a base station or a relay station; and(b) generates a reuse pattern, based on the mapped interference levels,including one or more reuse sets of stations, included in said one ormore stations, capable of sharing a transmission resource. In variousembodiments of the present invention, within each reuse set, thestations are listed in increasing order based on their respectiveinterference levels, and an additional station is added to a reuse set,as long as the cumulative interference level within the reuse set isbelow a threshold interference level and the additional station is notalready listed in another reuse set. In various embodiments of thepresent invention, the system removes empty reuse sets. In variousembodiments of the present invention, the system also generates anetwork schedule, by a network management entity, based on the reusepattern to increase bandwidth efficiency in the network.

Various embodiments of the present invention are applicable to IEEE802.16 networks, which includes amendments or extensions to IEEE 802.16.However, the present invention is not limited to IEEE 802.16 networks,and is applicable to other types of networks.

Similarly, various embodiments of the present invention are applicableto OFDMA networks. However, the present invention is not limited toOFDMA networks, and is applicable to other types of networks.

Various embodiments of the present invention are described herein withrespect to “mobile” stations that communicate with base stations andrelay stations in a network. However, the present invention is notlimited to networks with “mobile” stations. Instead, a network mighthave many different types of stations, typically referred to a“subscriber” stations, which communicate with base and/or relaystations. A “mobile” station is one type of “subscriber” station.

According to embodiments of the present invention, the above describedmethods, apparatuses and systems can, for example, mitigate the intranetinterference between different stations (either base stations or relaystations) operating within the wireless network (e.g., an OFDMAnetwork), thereby optimizing CINR degradation and thus allowing highercoding rates to be used on the impacted links, and cause a relatedimprovement on the spectral efficiency per link, considering theimprovement in the related bandwidth efficiency.

U.S. utility application titled “REUSE PATTERN NETWORK SCHEDULING USINGLOAD LEVELS”, U.S. Ser. No. 11/777,494, inventors Chenxi Zhu, Wei-PengChen, Jonathan Agre, Dorin Viorel and Jagan Seshadri, filed Jul. 13,2007, attorney docket number 1974.1019, and U.S. Provisional Applicationtitled “Load-Based MMR Network Scheduling Algorithm With FrequencyReuse”, U.S. Application Ser. No. 60/884,464, filed Jan. 11, 2007,inventors Chenxi Zhu, Dorin Viorel, Jagan Seshadri, Jonathan Agre andWei-Peng Chen, Attorney Docket No. 1974.1019P, and which areincorporated herein by reference in their entireties.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method comprising: generating, by an entity in a wireless network,a reuse set capable of sharing a transmission resource, wherein saidgenerating comprises: beginning with a respective station of a pluralityof stations in the network with a smallest interference level, addingthe respective station to the reuse set, and adding an additionalstation of the plurality of stations with a next lowest interferencelevel to the reuse set, as long as a cumulative interference levelwithin the reuse set is below a threshold interference level and theadditional station is not already assigned to another reuse set.
 2. Themethod as in claim 1, wherein the network is an Institute of Electricaland Electronics Engineers (IEEE) 802.16 system, and each of theplurality of stations is a base station or a relay station.
 3. Themethod of claim 1, further comprising: generating a plurality of reusesets; and removing empty reuse sets that include no stations.
 4. Themethod of claim 1, further comprising: generating a reuse patterncomprising one or a plurality of reuse sets; and generating a networkschedule, by a network management entity, based on the reuse pattern, toincrease bandwidth efficiency.
 5. The method of claim 1, wherein theplurality of stations includes at least one relay station.
 6. Anapparatus comprising: means for generating a reuse set capable ofsharing a transmission resource, wherein the means for generatingcomprises: means, beginning with a respective station of a plurality ofstations in the network with a smallest interference level, for addingthe respective station to the reuse set, and means for adding anadditional station of the plurality of stations with a next lowestinterference level to the reuse set, as long as a cumulativeinterference level within the reuse set is below a thresholdinterference level and the additional station is not already assigned toanother reuse set.
 7. A system for generating a reuse group oninterference levels in an Institute of Electrical and ElectronicsEngineers (IEEE) 802.16 network, comprising: means for generating areuse pattern capable of sharing a transmission resource, wherein themeans for generating comprises: means for adding an additional stationto a respective reuse set, as long as a cumulative interference levelwithin the respective reuse set is below a threshold interference leveland the additional station is not already assigned to another reuse set.